Lighting control devices incorporating sensors for estimating occupancy or vacancy are well known in the art. An example of such a device is a Watt Stopper WS-250 Passive Infrared Wall Switch Sensor (Watt Stopper, Santa Clara, Calif.), having both a load control device and a pyroelectric sensor in the same housing. Such devices typically use infrared and/or ultrasonic sensors that, when coupled with suitable signal conditioning and processing, are useful to detect signal changes that may indicate human motion in a space for estimating occupancy or vacancy. Typically, this sensed motion is used to control the on/off condition of a load, such as a light or air conditioner.
A load control system, for example, includes one or more load control devices (relays), that physically turn load circuits on and off, and one or more motion sensors. The motions sensors generate signals indicative of motion to the load control devices for the purpose of controlling the load circuits based on motion detected within a work space.
A lighting control devices and/or systems are often configured to turn on lights when motion is first sensed, and then turn off lights after a time delay that motion is no longer detected. This provides the benefits of conserving energy when the work space is unoccupied.